NAND Flash storage devices are used as non-volatile storage, and are characterized, among other properties by a writing process in which data is being written in units of pages into larger units of blocks. The nature and physics of such writing process and the risk to data associated with it are generally understood. The data-at-risk is likely to be damaged when the power to the storage device fails in the midst of writing, and the power applied to the memory is not stable. A power failure, in portable devices such as mobile phone, happens whenever the host unexpectedly turns the device off to save on battery life or the user removes the device.
One technique for reducing the risk of losing or corrupting data when power failures occur defines “risk zones” and manages the writing process to minimize the risk by avoiding risky areas or by backing up data in risky areas. However, this method of reducing the risk is wasteful in energy consumption and performance, because of the amount of data that may need to be backed up. The backup process consumes a high amount of energy (being a writing process) and reduces the performance (as the extra data writing takes time) of the storage device. Both the extra amount of time and the extra amount of energy are directly proportional to the amount of data needs to be backed up.